


Bone Appetit

by Nyarm



Category: Undertale (Video Game)
Genre: Bone-Licking, Cunnilingus, Ecto-Vagina, Fantasizing, M/M, Office Sex, Sanster, Vaginal Sex, gaster's a nerd
Language: English
Status: Completed
Published: 2016-05-22
Updated: 2016-05-22
Packaged: 2018-06-10 03:02:31
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,180
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6936775
Author URL: https://archiveofourown.org/users/Nyarm/pseuds/Nyarm
Summary: <blockquote class="userstuff">
              <p>Gaster notices his attraction to his little assistant.</p>
            </blockquote>





	Bone Appetit

**Author's Note:**

> my contribution to the sanster tag

After a week or so of intense thinking, Gaster believed he had finally uncovered the reason for his newfound fascination with his assistant, Sans. He quietly thought that it was unfortunate for him to realize this on his way to work where he would most definitely see the small skeleton, but he digresses. Yes, for the past several days Gaster had been beset with an infatuation for his dear little helper, though he hadn’t known it at the time. He didn’t quite understand how he, a fleshy, living monster, could be attracted to such grim reminder of mortality, but he was and, fuck, if it wasn’t irritating. Just thinking about Sans’ lazy grins and half-hooded eyes got him hot and bothered now and, ugh, he had it so bad. Hotland’s heat was getting to him a little and the hot air rolling off the glowing lava below him in waves was honestly making him feel a little feverish. Everything about Sans enticed him, he realized. He knew his young assistant’s laid back demeanor was a product of his laziness, but the languid way he carried himself was just so hot. He didn’t even know if skeletons could have sex, maybe they had sensitive bones? Gaster could feel himself get a little aroused at the thought, but was cut out of his reverie when he saw the titanic shadow of the lab fall over him.

When he stepped inside, a blast of cool air blew over him and he sighed in relief. It was a pain at the time, but installing an air-conditioner in the lab was inarguably one of his wiser choices. He walked through the main area, footsteps echoing off the grey tiles as he went, and snagged a black lab coat off the hook by the weird elevator. He’d always thought its exterior bore an uncanny resemblance to a bathroom. He pulled on his coat and buttoned it up while the elevator brought him down into the lower levels of the lab.The steady hum and clamor of machinery greeted him as he stepped out. Sans was already there, hunched over and checking on the machines’ colorful dials and meters, ensuring that everything was running fine.

“Hey, G, I placed those files you wanted over on your desk,” Sans drawled, straightening up before turning to face him. Gaster nodded, and couldn’t help but notice the fact that Sans wasn’t wearing a lab coat today and he looked so much smaller for it. Sans is so adorable, he thought. He couldn’t bring himself to scold his assistant, because the lack of a coat left Sans’ smooth white arm and neck bones on full display. He ran his tongue over his sharp teeth. Gaster felt a little gross, but he couldn’t help imagining how nice it would be lick between every crevice in Sans’ body, to hear Sans moan and whimper at his thorough exploration. His fantasizing led his eyes a bit lower before they settled on the skeleton’s sweatpants covered pelvis and, oh, he could only imagine how Sans would sound if he touched there-

“Hey, Gaster?” Sans was looking at the ground, flushed blue, “You okay? You, uh, haven’t said anything.” He shoved his hands in his pants pockets and glanced to the side, looking a bit flustered. The older scientist could not believe he just started fantasizing about Sans, in front of Sans. How embarrassing, he thought, what was he? Some kind of uncontrollable pervert?!

“Ah, i-it’s nothing, I merely became distracted for a second. Nothing to worry over,” Gaster sincerely hoped Sans bought that. He left before Sans could answer and shut himself in his office. He slumped against the door, the arousal from his fantasy lingering in his groin. He was feeling weirdly aroused and glanced down at his slacks. 

Oh. 

Oh, no. 

He had somehow worked himself up enough in those scant few seconds of daydreaming to give himself an erection. He buried his face in his hand embarrassed, a dark purple blush spreading over his face. Sans had seen. No wonder he was so flustered. 

Gaster dragged himself up from the floor and went to sit at his desk, mortification incarnate. He noticed that the files were on his desk just as Sans said, neatly stacked into cute color-coded folders. He could just imagine Sans trying to organize the papers so neatly, face scrunched up adorably in concentration. The thought of Sans made shame rush back into Gaster and he blushed hotly. He decided to get to work and sank into his rolling desk chair, shrugging off his lab coat. He successfully distracted himself by filling out paperwork and polishing his reports for a couple hours before twirling around in his desk chair a couple times, rubbing at his sore wrists, the little incident far from his mind. The carpet floor made it hard to gain much momentum, but Gaster tried his best. At the end of a particularly fun spin, a knock sounded at his door and he righted himself, trying to look professional.

Gaster cleared his throat, “Come in!” He called and in shuffled an embarrassed Sans. The little debacle from earlier rushed into the scientist’s brain and he felt his cheeks grow warm.

“D-do you need something?” He stuttered out. Sans took a step forward and shut the door behind him. 

“Heh, I just, uh, wanted to ask you about earlier. ‘Cause you were looking pretty bothered staring at me earlier” Oh, dear god, Gaster thought, the urge to die growing with every second. Maybe he should just jump into the core, then no one would know his shame.

“Do you want to bone me, doc? I mean, I wouldn’t mind showing you my boner,” the skeleton sounded confident, but looked just as flustered as Gaster felt. The pun was sadly ignored as Gaster shot out of his chair.

“Yes!” He blurted out and was in front of Sans before he could process what had happened. His assistant’s eyes widened a little as Gaster pulled him into a kiss, eager for whatever skeleton sex Sans had in mind, licking all over his teeth before pushing him down on the plush carpet floor. The younger formed a tongue to meet Gaster’s and the wet slide and slick noises made arousal hum in both. The tongue was a surprise, but the older scientist was not complaining. Sans made a noise into the kiss and the older scientist couldn’t help sliding his hands under the younger’s shirt. Sans whined and reciprocated the action as Gaster dragged his thumb up and down his sternum. Looks like he was right about the sensitive bones. Gaster moaned as well, feeling sharp phalanges drag across his skin was the best feeling in the world. Sans sat up, breaking the kiss, before tugging his shirt off altogether, exposing inch after inch of porcelain-like bone. His ribs and spine looked irresistible and Gaster couldn’t help but think back to his earlier fantasy.

“Can I lick you?” He asked, bluntly, and Sans’ dusky blue blush grew even deeper as he nodded furiously. 

“Bone appetit, G,” Sans said with a nervous chuckle.

Gaster couldn’t help but laugh as well. He pushed Sans back down and began to lave his tongue over his spine. The nooks and crannies of the warm bone excited him. The skeleton’s hands shot up to Gaster’s shoulders to cling on as he mewled, the rush of cool air on Sans’ now wet spine must have felt amazing. Installing that air conditioner really was a good idea. Gaster loved Sans’ sounds and moved lower along his spine before reaching the crest of the his assistant’s pelvis. He tugged at the sweatpants and was about to ask for permission, but Sans practically ripped them off before spreading his legs, eager. That’s so cute, Gaster thought, and his neglected cock throbbed in his pants. He fingered at the hole in the skeleton’s pelvis and Sans moaned loudly. Gaster smiled and dipped down to lick and suck at the edges of the bone while listening to the chorus and whines and moans above him. Sans’ hips bucked as his vibrant magic began to coalesce in his pelvis, forming a pussy. Gaster honestly did not know skeletons could do that, but refrained from commenting and began toying with Sans’ clit, familiar with this kind of anatomy. Sans gasped and rocked up into his hand as he rubbed along the labia and brushed his fingertips along the outside of the entrance. He bent down and licked along the length of the slit and he could see bony fingers grip onto the carpet as the younger gasped. Gaster traced the outside of Sans’ hole with his tongue and flicked it over his clit. Sans squeaked when he began sucking on the sensitive bud before pulling back and blowing cool air on it. He thrust his tongue inside and the taste was amazing, his assistant’s sweet little noises spurred him on his tongue-fucking.

The skeleton grew wetter and wetter as Gaster went on and the older scientist couldn’t help but unbutton his pants, eager to enter his precious assistant. He pulled back and rubbed slow circles into Sans’s firm little nub with his thumb before slipping a finger inside him. Gaster groaned slightly, the inside of the pussy was warm and smooth and wet and perfect. Sans whimpered at the slight penetration and propped himself up on his forearms. He sat up and scooted closer to Gaster until their legs overlapped, the scientist looked a little confused, but was still fingering him. The younger rubbed over the bulge in Gaster’s pants drawing a moan from him. He pulled the older man’s pants down a little and his partner humped into his hand when bone met hot flesh. Sans jacked Gaster off slow and steady and whimpered when another finger was added inside him. The sight of the man’s cock made him ache for it inside him and the fingers rubbing at his walls didn’t help. 

Sans pushed Gaster down and straddled him as his fingers slipped out. He braced himself and held onto the cock to position it before sliding onto it. The head popped in and San moaned, rocking back and forth to get the rest inside. Gaster’s dick was stretching so nicely and Sans could feel it twitch inside him as he settled on the scientist’s pelvis. 

Gaster was a bit stunned at how amazing it felt to have Sans wrapped around him like this. Sans started riding him and he could hear him moan and feel his pussy lips brush against his hips every time he bottomed out. Everything was so hot and slick and Gaster needed more. He gripped Sans’ hips and started thrusting up and into him as his little assistant gave a startled moan, stuttered by his thrusting. It was so good, he moaned loudly at the feeling of Sans’ slick cunt rubbing and caressing the hot flesh of his dick as he fucked into the skeleton. He pulled out of Sans and pushed him onto the floor again, caging him in with his body before slipping back inside. The younger scientist was a little surprised, but was quickly distracted by the insanely pleasurable feeling of Gaster pushing back inside him. Sans was being fucked much faster now as the older man had more leverage. He could feel the head of Gaster’s dick brush against his cervix and whined at the feeling. He was being fucked so much harder now and could feel Gaster brush against his clit at every thrust. Sans could feel himself getting closer and felt hyper aware of everything, the scrape of the carpet against his bones, Gaster’s hot breath, his own moans and noises. 

“Gonna cum, fuck, gonna cum,” Gaster panted against Sans’ shoulder, practically bashing their hips together. He kissed Sans again and his assistant squeaked into it, surprised, but kissed back fervently. The wet sounds of their kissing combined with the slapping of his hips against bone caused Gaster to thrust erratically, impossibly close to finish. He reached down to rub at the skeleton’s clit as he fucked into Sans’ pussy even harder. Sans gasped and whined loudly, wrapping his legs even tighter around Gaster’s hips before grinding down on his cock. Gaster thrust into Sans once, twice, before Sans broke the kiss and squealed, overcome, The feeling of Sans cumming around his dick, pussy fluttering and squeezing down on him caused Gaster to fuck into Sans even harder, carrying the skeleton through his peak before climaxing himself, letting out a loud groan as spurts of hot purple cum shot inside the younger as the older desperately fucked him through orgasm. Gaster’s thrusting died off and his hot panting mingled with Sans’ before he flopped alongside his assistant and pulled him in for a cuddle.

Sans nuzzled into his shoulder, and Gaster was about to say something about how cute he was, but was cut off by a small snore. Adorable. He sighed, maybe they could go again when Sans woke up.

**Author's Note:**

> ¯\\_(ツ)_/¯


End file.
